Process mass spectrometers typically have a number of conditioned gas samples, which are filtered and regulated to a small positive pressure, that are delivered on a continuous or intermittent basis. The gas inlet system associated with the spectrometer instrument often has two parts. The first part can be a multi-stream selector responsible for selecting one of the samples for analysis. The second part is responsible for taking the selected sample and delivering the sample into the vacuum of the mass spectrometer ion source. The delivery of the sample to the ion source requires taking a small fraction of the selected gas flow and reducing the pressure to be compatible with that of the ion source.
Typically, the pressure reduction is performed using capillaries and/or orifices as restriction elements to reduce the flow and pressure of the fraction of the sample. Often times, when the fraction of the sample is delivered to the ion source via small apertures, the pressure of the sample delivered to the ion source does not remain constant, especially when the incoming sample composition varies widely, and distortion of the sample can occur.
Accordingly, there is a need for a new gas inlet which allows for the delivery of a gas sample without distorting the composition and while maintaining a constant pressure within the ion source as the sample composition varies and providing rapid response to composition changes.